1. Field of the Invention
The present invention relates to a process for dissolving a sparingly water-soluble flavonoid.
2. Prior Art
Rutin, which is one of the typical sparingly water-soluble flavonoids, has pharmacological actions such as antioxidizing action, blood vessel reinforcing action and the like. Alternatively, rutin has been frequently used as an antifading agent for colored drinks. Where rutin is used as the antifading agent, it is desirable that at least about 0.01 W/V% of rutin be present in the aqueous solution. However, rutin is sparingly water-soluble, and its solubility is about 0.008 % in water at an ordinary temperature.
Some methods for dissolving rutin in water for pharmaceutical purpose are known, i.e., adding an aliphatic compound having an amino group to rutin (Japanese Published Examined Patent Application No. 1677/1950), and allowing a halogenated acetic acid or Rongalite to act on rutin for improving in its water-solubility (Japanese Published Examined Patent Application No. 2724/1951; No. 1285/1954).
Further, Japanese Published Examined Patent Application No. 32073/1979 has disclosed that reacting rutin with dextrin in the presence of transglycosidase gives a water-soluble product (a mixture of rutin, rutinglycoside, rutinmaltoside and rutinmaltotrioside).
However, it is not known that adding a small amount of a flavonoid analog to rutin improves the water-solubility of rutin.
In the case of using a sparingly water-soluble flavonoid such as rutin as an antifading agent for colored drinks, a method for dissolving the sparingly water-soluble flavonoid has been desired such that an antifading property of the agent is not affected, hygienic chemical problems do not arise in drinking, and a small amount of a dissolution enhancing agent can improve the water-solubility of the flavonoid to a desired degree.